Cameron F. Rae

Compact source of continuously and widely-tunable terahertz radiation.

We report a THz radiation source based on the technique of non-collinear phasematched parametric generation. The source, which is compact and operable at room temperature, generates nanosecond pulses of peak power and energy greater than 1W and 5 nJ respectively. The radiation is continuously tunable over the range 1.2-3.05 THz and is of narrow spectral bandwidth (<100 GHz). The use of intersecting pump and parametric wave cavities results in threshold pump pulse energies below 1 mJ (from a Nd:YAG laser excited at 20 W, 500 microsec by a quasi-CW diode-laser) and close to 50% down-conversion efficiency when operated at twice threshold.

Hyperspectral imaging of gases with a continuous-wave pump-enhanced optical parametric oscillator

We demonstrate a system for the active real-time hyperspectral imaging of gases using a combination of a compact, pump-enhanced, continuous-wave optical parametric oscillator as an all-solid-state mid-infrared source of coherent radiation and an electro-mechanical polygonal imager. The wide spectral coverage and high spectral resolution characteristics of this source means that the system is capable of being selectively tuned into the absorption features of a wide variety of gaseous species. As an example we show how the largest absorption coefficient exhibited by methane at 3057.7cm(-1) can be accessed (amongst others) and gas plumes imaged in concentrations as low as 30ppm.m using a parametric oscillator based on periodically-poled RbTiOAsO(4) (PP-RTA).

Line-narrowed, compact, and coherent source of widely tunable terahertz radiation

Parametric down-conversion techniques provide an effective means for producing terahertz radiation. A novel device, based on an intra-cavity geometry, has been developed that is both compact and widely tunable over the range 1-3 THz. Reduction of the free-running linewidth of this device (typically 50-100 GHz) to <5 GHz accompanied by continuous and smooth tuning over a band extending over 50-100 GHz where this band may be set anywhere within the above tuning range is described. A significant increase in the mean terahertz power generated to >10 muW is attained by increasing the pulse repetition rate up to 350 Hz. Applications in spectroscopy and imaging are discussed.

Polychromatic optical parametric generation by simultaneous phase matching over a large spectral bandwidth

The parametric generation of broad spectral bandwidths by the use of suitable phase-matching geometries is reported. Greater than 100-nm simultaneous bandwidth in the visible is generated in a collimated signal beam from a novel, noncollinear phase-matching geometry in a beta-barium borate optical parametric oscillator, which is pumped by the collimated output of a Q -switched and frequency-tripled Nd:YAG laser. Dispersive cavity tuning of the optical parametric oscillator by use of a rotatable Littrow-mounted grating, with a static crystal and pump configuration, is also described. A tunable bandwidth of >100 nm is also demonstrated.

Widely tunable all-solid-state optical parametric oscillator for the visible and near infrared.

An all-solid-state optical parametric oscillator (OPO) has been developed in which the signal and idler waves can be tuned over the ranges 455-665 and 760-1620 nm, respectively, with the potential for covering the entire range 420-2300 nm. The OPO uses a critical type I phase-matching geometry in lithium triborate and is pumped at 355 nm by frequency-tripled radiation from a diode-laser-pumped Nd:YAG laser. Oscillation thresholds (minimum 0.3 mJ), pump depletions (>35%), and linewidths of the OPO are reported.

Compact low-threshold Q-switched intracavity optical parametric oscillator

We report a singly resonant pulsed intracavity KTiOPO>(4) optical parametric oscillator that uses a semi-monolithic microchip laser design. The compact (50-mm-long), low-threshold (1.3-W) cavity uses a novel quadrupole deflector Q switch to give 4-microJ pulses at 1.064 microm and 0.4-microJ signal pulses of 5.6-ns duration at 1.53 microm with a repetition frequency of 5 kHz when it is pumped with a 2-W laser diode. The signal pulses are diffraction limited and single frequency.

A visible extended cavity diode laser for the undergraduate laboratory

We demonstrate how to construct a simple single-frequency extended cavity diode laser (ECDL) for the undergraduate laboratory using mainly standard opto-mechanical components. This ECDL is operated with both 635 and 670 nm laser diodes. We present three experiments that can be performed using this ECDL, namely spectroscopic studies of iodine, second harmonic generation, and an optical heterodyne experiment using the ECDL with a helium–neon laser.

Single-frequency, end-pumped Nd:YLF laser excited by a 12-mJ diode-laser array

We describe the operation of a diode-laser-pumped, end-pumped Nd:YLF laser that utilizes a 12-mJ, 60-W, quasicw diode-laser bar. Multilongitudinal-mode, TEM(00) pulse energies of greater than 2 mJ have been observed, with corresponding Q-switched peak output powers in excess of 118 kW. The incorporation of a prelase Q-switching technique has seen single-longitudinal-mode peak powers in excess of 90 kW continuing to be achieved. The low-threshold operation at 1.539 microm of a singly resonant KTP optical parametric oscillator pumped by this source is also reported.

Intracavity parametric generation of nanosecond terahertz radiation using quasi-phase-matching

We report the use of quasi-phase-matching techniques based on periodically-poled MgO:LiNbO(3) for the generation of nanosecond duration pulses of terahertz radiation in intracavity optical parametric oscillators. Multiple idler-waves are generated with temporal studies indicating that the initiating process is the expected parametric down-conversion, but followed by cascaded difference frequency generation. A number of grating geometries have been explored, revealing the presence of dual solutions for the quasi-phase-matching process in the general case. Choice of grating parameters so as to minimize oscillation threshold while simultaneously ensuring effective extraction of the THz radiation is considered.

An Intracavity Optical Parametric Oscillator With Very High Repetition Rate and Broad Tunability Based Upon Room Temperature Periodically Poled

We report a low-pump-threshold, very high-repetition-rate, singly resonant optical parametric oscillator (OPO) pumped internally to a diode-pumped, Q-switched Nd:YVO4 laser. The OPO, based upon a 27.0-32.5-mum periodically poled MgO:LiNbO3 crystal with fan grating design, exhibits a broad tunability range of 1.38-1.79 mum (Deltalambdas = 411 nm) and 2.62-4.64 mum (Deltalambdai = 2019 nm) in the signal and idler fields, respectively. For an external diode pump power of only 3 W, up to 150 mW of idler were extracted from the device or, when the signal field was output coupled, 330 and 100 mW of signal and idler, respectively, were simultaneously obtained. By taking advantage of the intracavity parametric cavity dumping process, repetition rates in excess of 350 kHz were achieved whilst maintaining high down-conversion efficiency. We demonstrate the potential of this device in spectroscopic applications with an absorption measurement of low concentration CH4.